Such devices are used to control gas exchange valves in such a way, that it becomes possible to operate reciprocating engines without the throttle valve that would otherwise be necessary.
Such a device is disclosed in DE 101 23 186 A1, for example. In this device, a rotating cam first drives a connecting link, which executes a pure oscillating rotary motion and carries a radial cam which is composed of a rest area and a lift area. The radial cam transfers the lifting curve necessary for actuation of the valve to the roller of a driven element similar to a cam follower which in turn actuates the valve. The desired different valve lifting curves are produced by the fact that the center of rotation of the connecting link is displaced on an arc-shaped path which is concentric to the roller of the driven element when it is in the position that it assumes when the valve is closed. The center of rotation is formed by a roller which is provided on the connecting link and which is supported in a non-positive manner on an arc-shaped track in the housing; this track is also concentric to the roller of the driven element, that is, it forms an equidistant to the path of the center of rotation and is designated as the courses. In addition, the roller on the connecting link is supported against a cam disk, whose angular position determines the position of the center of rotation on its arc-shaped path. However, the prior art device is encumbered by some disadvantages.
First, the roller on the connecting link only lies against the courses when the gas forces and inertial forces of the valve train are correspondingly oriented and the roller is actually supported on the courses. If this is not the case, which can happen when an overspeed occurs, for example, then the non-positive connection is lost and a liftoff occurs, which causes noise and even damage when it comes back down. In addition, it is relatively difficult to machine the coulisses, which are segments of an inside cylinder and cannot be machined in a continuous manner, and the commonly used housing materials are insufficiently hard for the contact between the roller and the courses. There is a disadvantage concerning mounting, which is that the valve gear housing cannot be set on the cylinder head in completely premounted form.
Other devices of this type have been disclosed in which the center of rotation of the connecting link driven by the cam is supposed to be adjusted on a circular path (OS 195 32 334 A1; EP 0 717 174 A1; DE 101 64 493 A1). However, the previous publications do not contain any teaching about how to construct the devices to realize such adjustment.
It is a common disadvantage of all devices that, due to manufacturing tolerances, as the valve strokes of the individual cylinders are reduced further for the purpose of controlling the load, the differences between the valve strokes of the individual cylinders become greater.
It is an object of the invention to create a device, which avoids the disadvantages of the prior art and allows secure control.